High on their list of policy goals is a tax on meat, akin to tobacco and alcohol "sin taxes."

The theory is that meat, especially beef, is disproportionately responsible for greenhouse gas emissions and if we were able to change how people eat, primarily in wealthier countries like the U.S., we could take a significant bite out of climate change.

A blueprint to achieve the meat tax is laid out in a November report by Chatham House, a London-based think tank. The group concedes that the issue is "complex."

Yet it advises governments to push for the taxes through publicly funded public relations campaigns which make the matter appear clear-cut, because "publics respond best to simple messages."

This is an unusual recommendation for a group known for promoting open debate.

Those backing the taxes cite the United Nation's Global Livestock Environmental Assessment Model, or GLEAM, which concluded in 2013 that livestock, including beef, milk production, and poultry, accounts for 15 percent of global greenhouse gas emissions.

However, the model was not developed as fodder for anti-meat campaigns, but rather as a tool to guide the livestock industry toward more sustainable production.

Using GLEAM as scientific evidence to argue against meat consumption is as far-fetched as it would be to fight organic agriculture because it relies on manure, a source of methane and nitrous oxide, both greenhouse gases. No wonder advocates want to keep their messaging simple.

The idea that reducing meat consumption would make both humans and the earth healthier is challenged by consideration of the environmental impact of alternatives.

So what would be the environmental impact if we did reduce our caloric intake and shifted to the U.S. government's dietary guidelines?

Researchers at Carnegie Mellon University evaluated just that. In a study published in Environment Systems and Decisions last month, such a change "increases energy use by 38 percent, blue water footprint by 10 percent, and GHG (greenhouse gas) emissions by 6 percent."

Or, as the British newspaper The Independent reported it, "Lettuce is 'three times worse than bacon' for emissions and vegetarian diets could be bad for environment."

Of course, replacing lettuce for meat and comparing emissions on a calorie-for-calorie basis is absurd. But it underscores a relevant point: meat is actually nutrient dense — and tasty.

The report explains, "these perhaps counterintuitive results are primarily due to USDA recommendations for greater caloric intake of fruits, vegetables, dairy and fish/seafood, which have relatively high resource use and emissions per calorie."

This isn't the first study to challenge the simplistic "meat is bad for the environment" claim.

According to a recent study from the University of Michigan's Center for Sustainable Systems, "An iso-caloric shift from the current average U.S. diet to USDA dietary recommendations could result in a 12 percent increase in diet-related GHG emissions, whereas a shift that includes a decrease in caloric intake, based on the needs of the population — assuming moderate activity, results in a small, 1 percent decrease in diet-related GHG emissions."

The lesson: if you want to advocate for meat taxes, follow the advice of the experts and keep it simple. Otherwise, the science will get in the way of your agenda.

Jeff Stier is director of the risk analysis division of the National Center for Public Policy Research, a conservative think tank. He earned his law degree from Benjamin N. Cardozo School of Law and served two terms as editor-in-chief of the Cardozo Law Forum. Readers may write him at 20 F Street, NW, Suite 700, Washington DC 20001. Follow him on Twitter @JeffAStier. This essay is available to Tribune News Service subscribers. Tribune did not subsidize the writing of this column; the opinions are those of the writer and do not necessarily represent the views of Tribune or its editors.